AROID IDENTIFICATION

“What is this plant?” and “what is this plant called?” feel like the same question. They are not, and they have different answers, arrived at by different means. The first is a question about the plant in front of you. The second is a question about two centuries of argument, conducted in print, about which name that plant is entitled to.

This section is about the second question. It is the one that makes a plant arrive under one name, appear in a monograph under another, and sit on a nursery bench under a third.

Where this sits

Two companion sections answer the other questions. Aroid Morphology is how to read the plant — the parts, what they are called, and which of them carry information. It already sets out the one vegetative feature a taxonomist reaches for first in each genus, so telling the genera apart is settled there and not repeated here. The Araceae tree is about relationship: which genera are each other's closest kin, and when they diverged.

What is left is the name itself. How a plant gets one. What the name is actually attached to. How far a key can carry you, and where it stops. Why the name changes, and what a changed name does and does not mean. And why the plant you bought is, more often than not, not a species at all.

The names move because the work is not finished

It is tempting to read a name change as a correction — someone got it wrong, someone else fixed it. Usually it is not that. It is a new piece of evidence arriving: a specimen refound, a molecular tree published, an older name noticed in a book nobody had read for a century.

The scale of that ongoing work is easy to underestimate. Counting only Aroideana, the journal of the International Aroid Society, and only since its first issue in 1978: 303 aroid names have been published or recombined in its pages — a new subfamily, two new genera, and among the species 105 Anthurium, 41 Philodendron, 29 Typhonium and 26 Amorphophallus. That is close to 8% of all accepted names in the family, from one society journal¹.

A botanical name looks like a label. It behaves like a legal instrument. Every part of it — including the parts most people skip — is doing work.

The part everyone skips

Take a name in ordinary use:

An author citation is not a courtesy. It is a pointer to a published description, in a stated place, on a stated date — and those three things are what makes a name checkable rather than merely asserted.

The specimen underneath

Here is the part that surprises people. A species name is not attached to a species. It is attached to one preserved specimen — the type — sitting in a named herbarium. The species is a hypothesis about which plants belong with that specimen. If the hypothesis changes, the name follows the specimen, not the idea.

For names published before herbarium practice settled, the anchor can be a picture. Dennstedt's 1818 name rests on plate 19 of van Rheede's Hortus Malabaricus — an engraving published in 1692². A name in daily use in nurseries today reaches back, through an unbroken chain of citation, to a seventeenth-century engraving.

And a picture can still be doing that job today. This is the type of Monstera punctulata — not a pressed specimen, but a nineteenth-century drawing from Schott's collection of aroid illustrations in Vienna. The specimen it was drawn from is gone; the drawing is what the name now hangs on⁹.

Why the older name wins

The rule is priority: among validly published names for the same plant, the earliest is the one to use. That is what put Dennstedt's 1818 name ahead of Arum campanulatum, Roxburgh's much better known binomial — and it did something sharper than merely outranking it. Roxburgh had himself cited Rheede's plate 19 in his synonymy. Citing the basis of an earlier name inside your own makes the new name illegitimate². Not merely second in line: not available at all.

This is why Amorphophallus campanulatus persists in older horticultural writing and is not the accepted name.

None of this is exotic. It is ordinary taxonomic housekeeping, and it is going on continuously — which is the subject of Part III.¹

A dichotomous key is a decision tree. At each step it offers two statements, you pick the one that matches, and it sends you either to another step or to a name. It is the oldest working instrument in taxonomy and it is astonishingly effective — inside its own limits, which are almost never printed on it.

A real one, from 2025

This is how a current key opens. It is the key to section Cardiolonchium — the velvet-leaved Anthurium — in the revision of that section for Carchi Province, Ecuador⁴:

Notice what the first three couplets actually ask for. Couplet 1 wants the position of the geniculum — a character the morphology guide covers — and then, in the same breath, it wants the province and the elevation. Couplet 3 wants to know what color the blade goes when it dries.

A living plant on a windowsill has no drying color, and it is not at 796 meters in Carchi. This key is not being coy about that: its title says from Carchi. It is a precision instrument for identifying pressed specimens collected in one province of Ecuador, and it is excellent at that. It was never a lookup table for a plant in a pot.

Keys that do not make you choose an order

The dichotomous key's other constraint is that it fixes the sequence. If couplet 1 asks about the fruit and your plant has never fruited, you are stopped at the first step, holding a plant with fifty other visible characters you are not permitted to use yet.

Multi-access keys invert this. You enter whatever characters you can actually see, in any order, and the set of candidates narrows as you go. The aroid family was an early subject: the CATE Araceae project at Kew built descriptions, images and interactive keys onto the web as part of a broader move to put descriptive taxonomy online⁵, and that work has continued since, growing to cover a large fraction of the two biggest genera.

Three ways to fail a key without noticing

All three produce a name. That is what makes them dangerous.

Keying the wrong stage. In Monstera the adult leaf — the thing everyone photographs — is the least reliable character in the genus, while the seedling and juvenile forms hold steady within a species. Key the adult and you are working from the most variable evidence the plant has. The Monstera guide is built around that inversion. Steady does not mean permanent, though: Tom Croat wrote on January 8th, 2007, that Monstera dubia definitely changes from its shingled, mottled juvenile leaves to preadult leaves that are solid green, and never reverts to the juvenile form¹⁷.

Keying one part of one leaf. Some characters vary from sector to sector within a single blade. A character that does that cannot separate two plants by which value it takes, because both plants show both values — it separates them only if one stops showing a value at all. The Alocasia guide works through the case in detail. Characters also vary between siblings: on August 16th, 2001, Michael Pascall wrote that seed of a strongly spotted-petiole form of Amorphophallus galbra gave him only one seedling with a spotted petiole, the rest all green, and that the only true way to identify these variable plants is by the flower¹⁸.

Keying something the key was never given. If the plant is a garden hybrid or a named cultivar, no key to wild species contains it, and every one of them will still return a species name. Which is Part IV. A plant from another genus is outside the set as well, and a label can hide that. Don Bittel wrote on June 22nd, 2000, that two tubers he had bought in California as Amorphophallus abyssinicus were Gonatopus, round and wide at the bottom and pointed on top like a pyramid. Wilbert Hetterscheid replied in the same thread the next day that Gonatopus is often mistaken for Amorphophallus in Africa, and that an Amorphophallus tuber usually has a noticeable depression on top where the bud rests, while Gonatopus is more pyramidal^19, 20.

A name change is rarely a correction. Almost always it is evidence arriving — a specimen refound, a tree published, an older name noticed in a book nobody had opened in a century. The plant has not changed. What is known about where it belongs has.

Four things move a name, and they move it in different ways and for different reasons. Telling them apart is most of what it takes to read a disagreement between two sources.

1 · The genus boundary moves

Sometimes a whole genus turns out to sit inside another one. When that happens every species in it needs a new combination, and the old genus name survives only as a synonym.

Pseudodracontium went this way in 2012, absorbed into Amorphophallus³. Furtadoa followed in 2025, absorbed into Homalomena, with two of its species recombined and Homalomena mixta returned to its original name. The standard references for the family were published between the 1990s and the 2000s, while both genera were still standing — which is exactly why a name looked up in a good book can be out of date without the book being wrong.

The move is not always clean. Pseudodracontium harmandii could not simply become Amorphophallus harmandii, because that name was already occupied by a different plant, so it needed a replacement and became Amorphophallus pseudoharmandii³. An awkward name is often the fossil of a collision like this one.

The boundary moves outward too, and that case is the more instructive one, because it shows a plant sitting under the wrong genus for nearly thirty years without anyone having made a mistake.

An aroid found in Sarawak in 1994 was described as Nephthytis bintuluensis — a startling record, because Nephthytis is otherwise entirely West African. It was put there because it matched. The Bornean plant differed from the African species in essentially one respect: it carries a single, very long-lived leaf and is only irregularly deciduous, sometimes leafless for long spells, where the African plants are evergreen creepers usually holding two or more leaves at once. On the characters available, Nephthytis was the right answer. When molecular data finally included it, the plant grouped not with African Nephthytis but with Asian Aglaonema — while the African species grouped with African Anchomanes. It was separated as a genus of its own, Boycea, in 2022¹³.

The resemblance had been pointing at the wrong continent. That is worth holding on to, because it is the same thing the measured result further down this page says in numbers.

2 · The species moves between groups

A species can keep its name and still move — from one section of a genus to another. Nothing about the binomial changes, so the move is easy to miss, and older sources go on saying the old thing indefinitely.

Anthurium clarinervium and Anthurium leuconeurum were placed in section Cardiolonchium, the velvet-leaved group, for decades. In 2025 both were moved out, to section Andiphilum⁴. The evidence was of two kinds: breeding work showed they cross readily with a range of other Mexican species but will not cross with typical Cardiolonchium, and molecular work separated them as well⁴. Most plant listings still say Cardiolonchium.

3 · The classification itself is tested

The largest kind of change is when someone asks whether the groups are groups at all.

The sections of Anthurium were set out on leaf shape, seed number and spadix form, and the arrangement growers know was laid out in 1983⁷. In 2019 the accepted classification — 18 sections and two series — was set against a molecular phylogeny of the genus. Seven of the twenty groups held. The rest were either not monophyletic or could not be tested with the sampling available⁶.

All four, on one sheet

Occasionally a single object carries the whole story. The painting below is Roxburgh's, numbered 248 in the Icones Roxburghianae. Read the writing on it from the bottom up and you have three names for one plant, applied in sequence over two centuries¹⁰.

4 · An older name surfaces

The last mechanism is the one Part I follows in detail: someone establishes that a different, earlier name has priority, or that the name in use was never legitimately published. The plant is unchanged, the group is unchanged, and the name still moves.

Even a revision of a whole genus can use an illegitimate name. Asked on the Aroid-L mailing list when and by whom Monstera pinnatipartita had been resurrected, Tom Croat answered on May 4th, 2022, that it must have been Michael Grayum, in a paper of 1997, and added that Madison's 1977 revision of Monstera had still included the plant as the illegitimate Monstera dilacerata, whose type turned out to be an Epipremnum from Southeast Asia²³. The published record is a little different: the name does belong to the Old World climber Epipremnum pinnatum, but its original material has not been found, and the type it carries is a neotype designated in 2018³⁰.

A 2024 case runs entirely inside Anthurium, and it turns on a decision taken in 1898. Two sectional names in Anthurium — Schizoplacium and Dactylophyllium, between them many but not all divided-leaved species: Schizoplacium with simple but dissected blades, and Dactylophyllium with radiately or condensed-pedately compound blades — were validly published in the same act, so neither is older and no date can separate them. The Code answers that situation by giving the decision to the first author who publishes a choice between them — and that choice, once published, holds permanently. Engler made it in 1898, when he treated Dactylophyllium as a synonym and kept Schizoplacium¹⁴.

In 2013, a hundred and fifteen years after Engler's choice, the two names were revisited by authors who understood the choice to be still open to them, and who anchored Schizoplacium to the single species in it that the authors' unpublished molecular work places inside the Dactylophyllium group. That welded the two names together: on current evidence they name one section, and the name it must carry is the one Engler chose¹⁴.

Nothing about any plant changed. The name moved because of a sentence written in 1898 and a specimen chosen in 2013. Dactylophyllium has a reasonable taxonomic claim, but Schizoplacium must prevail on nomenclatural grounds¹⁴.

None of this is unusual, and none of it is a sign of a field in disarray. It is the ordinary rate of work in a family where new species are still being described in quantity every year¹ — and where a good deal of what is in cultivation has never been through the process at all. Which is Part IV.

Everything so far has been about wild species and the names attached to them. Most plants in cultivation are not wild species, and no amount of keying will make them into one.

Three different kinds of thing

A species is a wild population with a Latin binomial and a type specimen. A hybrid is the offspring of two species. A cultivar is a selected plant maintained by propagation — often a single individual, cloned indefinitely, so that every plant bearing the name is in a real sense the same plant.

A species name can also be in use before the plant has been found in the wild. Alocasia reginula was long known only from cultivation; Peter Boyce wrote on November 7th, 2003, that it had been found in the wild in Borneo, and on January 25th, 2009, that it had been found on the Tabin limestones of eastern Sabah^24, 25. Alocasia nebula, which received its formal name in 2000, was still unknown in the wild when he wrote on January 25th, 2009: he, Josef Bogner and Alistair Hay had each seen it growing as a planted specimen at Semenggoh near Kuching in the mid-1990s, and none of the staff they asked was sure where it came from²⁵.

Nor does propagation always copy a plant exactly. Alocasia ‘Polly’ began in the 1980s, when one plant among the tissue-cultured Alocasia ‘Amazonica’ liners at Silver Krome Gardens showed heavier leaf substance, shorter petioles, better shipping qualities and slower growth than the standard plants. Bill Rotolante, in a note Steve Lucas relayed to the Aroid-L mailing list on November 19th, 2009, called it a sport created by genetic changes in tissue culture²⁶.

The three kinds are written differently, and the writing tells you which you have:

What the parentage does to identification

Take a real group of named plants, published with their parentages⁸:

All five were published as crosses with the same parent, Alocasia odora, and all five came from one introducer⁸. They carry a family resemblance to each other and to that shared parent which has nothing to do with wild relationship. Run any of them through a key to wild Alocasia and it will return a species name, because a key has no way of saying this is not a wild plant.

And then read the third column

Fifteen years later, three of those five names no longer mean what they did, in two different ways.

Two were renamed and the old name kept as a pointer. ‘Purple Moon’ is now ‘Robudora’, and ‘Shimmering Velvet’ is now ‘Regal Shields’. Both superseded names are recorded against the current entry, so a plant that arrived under the old label can still be traced.

The third was not renamed at all. Alocasia ‘Manta Ray’ is still in use — for a different cross. The plant sold under that name is now recorded as Alocasia macrorrhizos ‘Borneo Giant’ × Alocasia nycteris, while the 2010 cross is called ‘Nyctedora’. The label stayed and the plant behind it changed.

The same list shows how a trade name behaves. Alocasia nycteris is a species, and it moves in the trade as 'Bat Wing'⁸. A name in quotes on a label may be a published cultivar, an unpublished selection, or a marketing name for an ordinary species — and the label looks identical in all three cases. On July 12th, 2001, Eduardo G. Gonçalves wrote that the name Philodendron ‘Santa Leopoldina’ is not formally recognized and is used for at least three different plants, one of them the species Philodendron spiritus-sancti, and that a seedling of Philodendron atabapoense could be sold under it; he warned against paying US$300 for one²⁷.

A species name can also hide a hybrid, with no quotation marks to give it away. Peter Boyce wrote on December 3rd, 1997, that he had never seen a true Arum maculatum with silver veining and judged a correspondent's plants to be probably Arum italicum subsp. italicum or hybrids between the two; the check he gave is when the plants break growth, late summer or early fall for Arum italicum and winter to late winter for Arum maculatum²⁸. Seed carries the same risk: on May 3rd, 2008, Julius Boos wrote that photographs from at least two growers had led him to believe that plants raised from seed shared in 2004 from one plant of Cyrtosperma cuspidispathum were hybrids, and reasoned that insects had carried pollen onto the mother plant from one of the hybrid Cyrtosperma grown in the same greenhouse²⁹.

What makes a cultivar name real

A cultivar name is not real because a nursery uses it. The rules are set out in the International Code of Nomenclature for Cultivated Plants, and they are stricter than most people expect. A cultivar, in the Code's own words, is an assemblage of plants that "has been selected for a particular character or combination of characters" and "remains distinct, uniform, and stable in these characters when propagated by appropriate means"¹¹.

To become established, the name must be published with a description, in dated, printed matter distributed to the public or to institutions with libraries. An undated catalog does not establish a name. And — the part that surprises everyone — electronic publication does not establish a name: not a website, not a post¹¹. A trade catalog that exists only online can be made to count, but only by printing it and depositing two copies in a designated library¹¹.

Which is why so many plants in circulation carry names that look formal and are not. Alocasia shows the scale: 92 species are currently accepted in the genus, while the Aroid Archive lists 288 named hybrids and 221 named cultivars. Not one of those names appears in any key in Part II, because none of those keys was written to contain them.

There is no registry that issues plant names and no office that approves them. There are publications, and there are people who read the publications and form a view. Knowing which of those you are looking at is most of the skill.

Four resources, doing four different jobs

They are routinely treated as interchangeable. They are not, and the differences are exactly where mistakes happen.

The family has also had its own effort at putting descriptive taxonomy online rather than leaving it in print: the CATE Araceae project, building descriptions, images and interactive keys onto the web with the aroid community's involvement⁵. Part II covers what that changes about keying.

“Accepted” is a judgment with a date on it

This is the part most worth internalizing. When a checklist says a name is accepted, it is not reporting a measurement. It is reporting that the people maintaining it have read the published arguments and formed a view. Two careful authorities can hold different views of the same plant and both be honest, because the disagreement is about how much difference makes a species — which is not a question evidence alone settles.

So a name is never simply right. It is accepted by someone, as of some date, on some published argument. When two sources disagree, those three things are what to compare.

The same dependence on evidence holds when the question is a living plant rather than a name already in print. Julius Boos, writing from Florida on the Aroid-L mailing list on July 29th, 2007, described what a taxonomist normally needs in order to put a name on a plant: a mature plant as a specimen, or better a series of specimens, with good collecting data attached¹⁶. In rare cases a series of good photographs can stand in, but they must show an adult plant and its inflorescence, and should include close-ups of the spadix at male anthesis. The examiner also wants to look closely at both sides of the leaf blade, the petiole and the rhizome. Without collecting data, he held, an identification by anyone is an educated guess. His advice was to photograph the adult leaves, petioles and rhizome, then grow the plant until it blooms and photograph the sexual parts with part of the spathe cut away; with that in hand, he wrote, Thomas Croat and Peter Boyce, whom he named as two of the world's leading experts on most aroid genera, may be able to give an accurate identification¹⁶.

How fast this actually moves

It is easy to imagine the naming of a well-known ornamental family as long settled. Counting only currently accepted species, and only those described since 2020:

Roughly a quarter of the accepted species of Anthurium, and over a third of Monstera, have been described in the last few years. A monograph from the 1990s is not wrong; it is describing a smaller genus than the one that exists now.

Binomial

The two-part name: genus plus species epithet. Anthurium clarinervium is a binomial; Anthurium alone is not.

Epithet

The second word. It has no independent existence — it belongs to a genus, and it travels with the species if the species moves.

Author citation

The name or names printed after the binomial. Not a courtesy: a pointer to the published description that made the name valid.

Basionym

The earlier name an epithet came from, when a species has been moved. The reason an author citation carries a name in parentheses.

Combination

A name made by moving an existing epithet into a different genus. The person who does it is cited after the parenthesis.

Type

The single preserved specimen — or, for some old names, an illustration — that a name is permanently attached to. The species is a hypothesis about what belongs with the type.

Holotype / isotype

The one specimen the author designated, and duplicates of the same gathering distributed to other herbaria.

Protologue

Everything published with a name when it first appeared — description, illustration, specimens cited. The primary evidence for what the name was meant to denote.

Priority

The rule that among validly published names for the same plant, the earliest is the one to use.

Illegitimate name

A name that was published but is not available for use, because of a defect in how it was published — for instance citing the basis of an earlier name inside it.

Homonym

The same name used for two different plants. Only one can stand; the other needs replacing.

Replacement name

A new name coined because the obvious one is already occupied. Often the explanation for an awkward-looking epithet.

Synonym

A name for a plant that is now called something else. A synonym is not an error; it is a name that lost priority or a group that was merged.

Accepted name

The name a given authority currently treats as correct. A judgment, held by someone, as of a date.

Section

A named group of species inside a genus, below genus and above species. Sections are hypotheses and are regularly revised.

Monophyletic

Containing an ancestor and all of its descendants. A group that fails this test is not wrong to use, but it is not a natural group.

Homoplasy

The same form arising independently in unrelated lineages. A homoplasious character can still identify a plant reliably; it just does not indicate relationship.

Dichotomous key

An identification tool built of paired statements, each choice committing you to a branch until you reach a name.

Couplet

One such pair, numbered, conventionally written 1a and 1b.

Multi-access key

A key that lets you enter whatever characters you can see, in any order, narrowing the candidates as you go rather than fixing the sequence in advance.

Cultivar

A selected plant maintained by propagation, its name written upright and capitalized in single quotes. Frequently a single clone.

Hybrid

The offspring of two species. Written with a multiplication sign between the parents, or given a cultivar name of its own.

Trade name

A selling name. It may look exactly like a cultivar name and carry none of the same obligations.

This hub is about names in general. The work of actually reaching one happens genus by genus, because every genus has its own keys, its own contested groups, and its own characters that look diagnostic and are not.

Five genera have a guide. They are not five versions of the same page — each one is built around the particular thing that makes that genus hard, and those things turn out to be entirely different from each other.

The rest of the family

More genera will follow. A guide goes up when there is something specific to say about identifying that genus — a key worth running, a contested group worth explaining, a character that misleads. Until then, the two companion sections carry most of what is needed.

Aroid Morphology is the vocabulary. Nearly every couplet in every key on this page is asking about a structure described there — the geniculum, the collective vein, the cataphyll, the sinus — and its genus-by-genus table gives the single vegetative character a taxonomist reaches for first in each genus. If a key asks something you cannot answer, that is usually where the answer is.

The Araceae tree is the other half of Part III. When a section fails a monophyly test or a genus is dissolved into another, the tree is the picture of what replaced it.

And Aroid Reproduction covers the flowering biology that sits behind several of the arguments here — including the crossing experiments that moved two well-known Anthurium species out of the section they had been in for decades.

Thirty sources carry this hub. Two of them — a short essay and a two-page nomenclatural proposal — do more work than their length suggests, and both are worth reading whole.